Now, I have little personal experience, and I'm not an expert; but I /have/ seen people lose their jobs due to their performance being diminished because of habitual marijuana use. I've never seen anyone lose a job because of caffeine.
I mean, I know plenty of people who use marijuana occasionally on the weekends and seem no worse for wear; from my understanding, it's not as bad as alcohol, and you may be right that it's not addictive, but it's certainly more harmful than Caffeine.
>but it doesn't change the fact that if you cut it out for a few weeks, you'd be more productive without the cost, dependency or negative side effects of coffee.
This is not true for me. Personally, I tend to ramp up my caffeine use slowly over a number of months, because I do develop a resistance. During these months, I am /significantly/ more effective than without caffeine, even if I quit for months.
Now, I do build up a resistance, so every few months I quit for a while, as I do eventually get to the point where I have diminishing returns. For me, this doesn't result in headaches, just a few days of more sleep than usual and reduced performance. Assuming I get my 12 hours a day of sleep, the reduced performance is still much better than, say, a hangover. I'm up to baseline performance within a week. (my baseline performance is /significantly/ lower than my caffeinated performance.)